1. Field of the Invention
The present invention relates generally to a document scanner. having automatic document feeder, and in particular to a document scanner with a light focusing device downward formed on the top glass panel of the scanner casing of the document scanner.
2. Description of the Prior Art
Document scanners are widely used to form image based electronic files of documents. The document scanners are generally categorized as reflective type and transmissive type. A typical reflective document seamier comprises a chassis arranged inside a scanner casing. The chassis comprises a light source projecting light onto a document to be scanned. The light is reflected by the document that is being scanned and received by an image sensing device. The image sensing device receives the reflected light and forms an image of the document. A typical example of the image sensing device is a Charge Coupling Device (CCD). The reflective document scanners are generally employed to scan document printed on a substrate that is not light transmitting.
The scanner casing of the document scanner comprises a light transmitting top glass panel on which the document to be scanned can be positioned. A non-light-transmitting cover is mounted to the scanner casing for selectively covering the top glass panel. In a scanning operation, the chassis is moved in a predetermined direction in a controlled manner. The light emitting from the light source is projected onto the document and then reflected back to the image sensing device whereby an image of the document is read by the image sensing device.
Some of the document scanners are equipped with a document feeder. FIGS. 1-3 of the attached drawings show an example of the document scanners that are equipped with a document feeder. As shown in FIGS. 1-3, the document scanner comprises a scanner casing 1 having a top panel 11 partly constituted by a light transmitting top glass panel 12. A document feeder 2 is mounted on and covering the top panel 12, as well as the light transmitting top glass panel 12, of the scanner casing 1.
The document feeder 2 comprises a casing (not labeled) inside which a driving roller 21 is rotatably mounted. A document passage 22 is defined around the roller 21. Inlet and outlet openings I and II are defined in the casing of the document feeder 2 through which a document 3 to be scanned is fed into and out of the document feeder 2. The document 3 that is fed into the document feeder 2 is driven by the roller 21 to move through the passage 22 from the inlet opening I toward the outlet opening II. The document feeder 2 has a bottom panel 20 in which a scanning window 23 is formed.
Also referring to FIG. 4, the document scanner comprises a chassis 13 comprising a light source 14 and an image sensing device 15, such as a Charge Coupling Device (CCD). When the document 3 is fed through the document feeder 2, a light 4 emitted from the light source 14 is projected onto the document 3 through the light-transmitting top glass panel 12 and the scanning window 23. The light is reflected by the document 3 and received by the image sensing device 15. An image of the document is thus formed by the image sensing device 15.
Conventionally, the light-transmitting top glass panel 12 is a flat board having opposite surfaces that are substantially planar. Such a flat board allows light to transmit therethrough However, the flat board is not capable to more effectively focus the light onto the document 3 to improve the scanning result. Conventionally, the issue is addressed by increasing the power of the light source or incorporating additional reflectors inside the scanner casing of the document scanner to improve the scanning result. Such solutions, although effective in improving scanning result, increase costs by either consuming more power or requiring additional parts.
It is thus desired to provide a document scanner having light focusing device for overcoming the above problems.